The present invention relates to methods and equipment for pressure shaping of metals and more particularly to methods for shaping parts by hydraulic extrusion and devices utilizing such methods.
This invention may find application in various branches of mechanical engineering where it may be required to obtain complex-shaped parts, such as, for instance, convexo-concave pieces, with walls of uniform thickness.
It is widely practiced in the art to shape parts by hydraulic extrusion whereby a blank is deformed by water supplied under pressure.
It is likewise known in the art to employ hydraulic extruders comprising a vessel communicating with a source of pressurized liquid supply the blank being mounted on said vessel, and clamping means fastening the blank about the outer periphery thereof to the vessel. Besides, a die with a cavity shaped like the desired part is mounted on the blank. The clamping means in the known extruder is constituted by a plate with a hole or a ring arranged intermediate the vessel and the blank so as to press the blank edge against the die.
The pressure of the blank against the vessel is to provide for the tightness of the vessel through the entire process of part shaping. This pressing force is provided in the known extruders by hydraulic presses or special devices formed as massive trusses coupled with hydraulic cylinders.
The die of the known extruder is generally made of steel or concrete reinforced with steel elements which provide the required degree of stiffness and which enable the die to withstand the force of pressure thereof against the vessel as well as the pressure of the liquid at the final instant of blank deformation when the blank comes into contact with the die. The cavity of the die is vented to the atmosphere to remove air in the process of part formation.
Extruding parts by the known method in the known extruder, pressurized liquid is supplied into the vessel and the pressure of the liquid is gradually raised to the value required to deform the blank. The blank edge clamped between the die and the vessel is likewise deformed, becoming smaller, thicker and forming folds or corrugations. The linear displacement of the blank edge is determined by the extrusion ratio set for each kind of material depending on its mechanical properties, as well as on the size of the part and the thickness of the blank.
The liquid transmits to the blank a pressure which is constant over its entire surface. The shape of the blank in the process of extrusion, before it is pressed against the die, is set randomly depending on the size of the blank and the mechanical properties of the blank material.
The known method for shaping parts by hydraulic extrusion has limited application for the reason that the parts manufactured thereby have walls manifestly differing in thickness. The wall thickness non-uniformity reaches 45 percent, with the corresponding deterioration of quality. According to the known method, extrusion is usually carried out at such pressures of the liquid as would permit avoiding loss of stability -- folding -- in the blank zone adjacent the clamping means. To this end, the pressure in the vessel is raised so as to slightly exceed the value required to deform the central portion of the blank, with the result that the blank material is thinned non-uniformly in the process of extrusion. This constitutes a material drawback of the known method for shaping parts by hydraulic extrusion.
The known hydraulic extruder has further disadvantages, among other things, the unavoidable need for a die. The latter is usually very bulky and heavy; furthermore, the die is extremely labour-intensive in manufacture as the surface of its cavity is to be finished to allow for an elastic springback of the part after the deforming load as springback of the part after the deforming load has been relieved.
Another disadvantage of the known extruder consists in that, to put up the necessary force to press the blank to the vessel and the die to the blank, it takes either powerful hydraulic equipment or special clamping means which are to be manufactured specially for each part size and for each kind of material. For this purpose use is made of screw jacks or hydraulic cylinder mounted at various points about the periphery of the blank. Therefore, in the process of extrusion, the edges of the blank are pressed non-uniformly which constitutes a quality risk.
Besides, with this arrangement, the pressing force control in the process of extrusion is a difficult matter.
It is an object of the invention to provide such a method of shaping parts by hydraulic extrusion which would yield complex-shaped parts with walls of uniform thickness.
It is another object of the invention to provide a hydraulic extruder wherein liquid would be supplied to different blank zones at different pressures.
It is a further object of the invention to provide a hydraulic extruder of a fairly simple and reliable design.
With these objects in view, there is provided a method for shaping parts by hydraulic extrusion whereby blanks are profiled by liquid supplied under pressure, wherein, in accordance with the invention, liquid is supplied simultaneously to different zones of the blank at different pressures corresponding to the desired part shape which is periodically checked as it is evolving in the process of extrusion.
To implement the method of the invention and to attain the foregoing objectives, there is provided a device comprising a vessel, which communicates with a source of pressurized liquid supply and whereon the blank is mounted, as well as clamps to fasten the blank to the vessel about the periphery thereof. In accordance with the invention, in the head of the vessel there is installed with one end thereof a guide member carrying a plurality of auxiliary vessels sequentially arranged so as to reciprocate freely along the guide member and adapted to fit one into another. The edges of these auxiliary vessels are pressed against the blank so that each pair of adjacent vessels defines with the blank a hermetically sealed cavity, each cavity being hydraulically connected to the pressurized liquid supply. The areas of the outer and inner surfaces of each auxiliary vessel are determined by the difference in the loads exerted thereupon by the pressure of the liquid in said cavities adjoining the vessel on both sides so that the load inside the vessel is somewhat smaller than that outside the vessel.
In a device of this design, liquid may be supplied to different blank zones defined by the edges of the auxiliary vessels at different pressures to obtain parts with walls of uniform thickness.
If the part to be manufactured has an intricate shape comprising, for example, numerous mating convex and concave surfaces, it is preferred that the device should include, mounted on the blank, a vessel, such as the one described hereinabove. In the head of the vessel there is installed with one end thereof a guide member carrying a plurality of auxiliary vessels arranged so as to reciprocate freely therealong, said auxiliary vessels being adapted to fit one into another. The edges of said auxiliary vessels are clamped in the blank in the interspaces between the edges of the auxiliary vessels disposed beneath the blank so that each pair of adjacent vessels defines with the blank a hermetically sealed cavity, each cavity being hydraulically connected to the source of pressurized liquid supply. The areas of the outer and inner surfaces of each of the auxiliary vessels are determined by the difference in the loads exerted thereupon by the pressure of the liquid in the cavities adjoining the vessel on both sides so that the load inside the vessel is somewhat smaller than that outside the vessel.
In one embodiment of the invention, the guide member to carry the auxiliary vessels reciprocating therealong is constituted by a hollow bar connected to the movable member of a hydraulic cylinder, and carrying, sequentially fitted thereover, a plurality of springs which constrain the auxiliary vessels to stay at a certain distance one from another and which also serve to press the auxiliary vessels to the blank prior to the start of operating.
If the dimensions of the part in plan are smaller than those of the vessel, it is preferred that between the vessel and the blank there should be positioned at least one plate fastened to the blank and to the vessel by a clamp and having a hole to fit the contour of the part in plan.
Each of the auxiliary vessels disposed above the blank should preferably house a conduit rigidly connected thereto, which conduit is intended to vent the air out of the vessel as it is being filled with the liquid. The conduit has an outlet close to the edge of the vessel and comprises a portion extending beyond the confines of the extruder parallel to the guide member and equipped with a valve which serves, inter alia, to monitor the displacements of the auxiliary vessel in the process of blank deformation.
In an alternative embodiment of the invention, each of the auxiliary vessels has a bushing adjacent the head thereof, which bushing is fitted over the guide bar and carries a spring constraining the auxiliary vessels to stay apart one from another, the bushings of adjacent additional vessels being adapted to telescopically fit one into another.
These bushings may be used to vary the areas of the inner or outer surfaces of the auxiliary vessels to comply with the abovementioned ratio of the loads exerted by the pressure of the liquid thereupon.